RU2141449C1 - Method of purification of natural graphite - Google Patents

Abstract

FIELD: preparation of construction materials in atomic power engineering and heat technology. SUBSTANCE: natural graphite is mixed with aqueous alkali solution, e.g. 40- 80% NaOH solution, sintered in furnace under stirring at 850 C for 3 hours. Product is placed into pulsation column. Dilute acid, e. g. 5.0-7.0% HNO₃, is fed upwards at rate of 1.7-3.0 m/h. Specific acid consumption is 5 1/kg of graphite. Pulse frequency is 25-35 pulses per minute. On completion of acid washing, graphite is washed with water in the same pulsating mode. Precipitate is separated on nutch filter, dried at 200 C. Graphite ash content is reduced from 7% to 0.04-0.48. Process power capacity becomes lower. EFFECT: more efficient purification method. 5 cl, 1 ex, 1 tbl

Description

 The invention relates to the technology of carbon-graphite materials, in particular to the production of low-ash graphite, which can be used as a structural material in nuclear energy, heat engineering, etc., as well as feedstock for producing colloidal graphite, graphite oxide and expanded graphite.

 A known method of purification of graphite with an ash content of 3.26-4.3%, which consists in processing graphite in an autoclave with a 10-20% alkali solution under a pressure of 12-15 atm. subsequent neutralization of 6% HCl with a mass ratio of graphite and HCl equal to 1: 4, washing with distilled water and drying; the resulting product is subjected to re-treatment in an autoclave at a mass ratio of graphite and alkali of 1: 4. As a result, graphite is obtained with an ash content of up to 0.02% [SU, 195433, C 01 B 31/04, 04.05.67].

 The specified method requires sophisticated technical equipment and high material costs, it is not productive enough unsafe.

A known method of purification of graphite, including sintering of graphite powder with Na ₂ CO ₃ at 900 ^o C, washing with water, then 5% H ₂ SO ₄ and subsequent magnetodynamic treatment at a magnetic field strength of 60-11 kA / m and a suspension mixing speed of 2-8 m / s; then the product is washed with water and dried. The result is graphite with an ash content of up to 1%. [SU, 1599303 A1, C 01 B 31/04, 10.15.90].

 The disadvantage of this method is the grinding of coarse graphite in the process of magnetodynamic processing and a high ash content in the final product.

The closest is a method of purification of ash graphite, including its treatment with an aqueous solution of Na ₂ CO ₃ at 900-950 ^o C, subsequent cooling of the cake, washing it with hot water, then 5% solution of H ₂ SO ₄ , cold water and drying the purified graphite. The result is graphite with a degree of purification of 99.2-99.6%. [SU, 168129, C 01 B 31/04, 11/18/65].

The disadvantage of this method is the high energy intensity of the method, associated with the need to conduct the process at a temperature of 900 ^o C and leading to high material costs, as well as insufficiently high degree of purification of high-ash graphite.

 An object of the invention is to reduce material costs and increase the degree of purification of high-ash graphite.

The problem is solved in that in a method for purifying natural graphite, including sintering graphite powder with an aqueous solution of an alkaline agent, subsequent washing with water and dilute acid and drying, washing the graphite with a countercurrent pulsating flow of the washing solution supplied at a speed of 1.7-3.0 m / h, and a pulsation frequency of 25-35 pulses per minute with a specific flow rate of 5 l / kg of graphite, 40-50% alkali solution is used as an alkaline agent, sintering is carried out at 350 ^o C; 5.0-7.5% nitric acid is used as the diluted acid, and the graphite washing after sintering is carried out first with diluted acid and then with water.

 According to the proposed method, after sintering of graphite with alkali, the washing is carried out by a countercurrent pulsating flow of the washing solution supplied at a speed of 1.7-3.0 m / h, with a pulsation frequency of 25-35 pulses per minute at a specific flow rate of 5 l / kg of graphite. A decrease in the flow rate <1.7 m / h leads to a decrease in the productivity of the process and thereby an increase in material costs, an increase in speed> 3.0 m / h leads to an increased consumption of the washing solution and adversely affects the degree of purification of graphite; reducing the pulsation frequency <25 pulses per minute reduces the washing efficiency, increases the ash content of graphite and the flow rate of the washing solution; an increase in pulsations> 35 pulses per minute is also impractical, since it leads to grinding of graphite during washing and deterioration of its quality.

 The most optimal flow rate of the washing solution is 5 l per kg of graphite. The decrease in these costs <5 l / kg leads to an increase in the residual ash content of graphite, and its increase> 5 l / kg is impractical, as it increases material costs.

The use of a 40-50% alkali solution as an alkaline agent can significantly reduce the sintering temperature: from 950 to 350 ^o C and thereby significantly reduce the energy consumption of the process.

According to the invention, 5.0-7.5% HNO _{3 is} used in the washing process. The use of a solution of nitric acid of the indicated concentration helps to increase the washing efficiency, accelerates the dissolution of ash products of sintering and allows to reduce the total specific flow rate of the washing flow rate of diluted acid. A change in the washing efficiency and lowering the cost of washing solutions is also facilitated by a change in the sequence of use of washing solutions: first, acid, and then water.

 In the proposed method, the graphite washing operation is carried out in countercurrent mode with pulsating phase mixing, such a washing process is based on the laws of diffusive mass transfer, practically does not depend on the degree of condensation of the sample, and is determined by the efficiency of the phase interaction: graphite suspension and washing solution in a vertical stream. Favorable conditions for the purification of graphite are also created due to the imposition of reciprocating oscillatory movements of the vertical flow of the washing solution, with a pulsation frequency of 25-35 pulses per minute, created by the pulsator: supplying compressed air in portions in a certain periodic mode.

 Example 1

1 kg of natural graphite brand GT-1 (GOST 4596-75) with an ash content of 7% is mixed with 0.48 kg (~ 296 ml) of a 50% NaOH solution and sintered in an oven with stirring for 3 hours at 350 ^o C. Next, the resulting product is discharged into the receiving device of the pulsation column located in its upper part. A 6.5% HNO ₃ solution with a temperature of 80 ^o C, with a flow rate of 5 l per kg of graphite, with a speed of 2.6 m / h and a pulsation frequency of the vertical flow of the wash solution of 30 pulses per minute is supplied counterflow to the bottom of the column. The excess alkali and the main part of the products of sintering of ash impurities are dissolved in dilute acid, carried out in a stream to the upper part of the column and in the form of acid-soluble compounds are discharged through a drain hole. Graphite descends gradually down the apparatus, where it is mixed with newly incoming portions of the acid wash solution and in the form of a graphite suspension in dilute HNO ₃ (mass ratio of graphite: HNO ₃ solution = 1: 3) is discharged into the lower chamber of the pulsation column and then enters the reactor with a stirrer for further acid treatment.

A suspension of graphite is mixed for 30 minutes at 90 ^o C for deeper purification from impurities. From the reactor, the graphite suspension is fed into a pulsation column for washing with hot (90 ^o C) water, supplied at a speed of 2.0 m / h, a pulsation frequency of 30 pulses per minute and a flow rate of 5 l per kg of graphite. Then graphite is discharged from the lower chamber of the pulsation column and fed to a suction filter, filtered and dried at 200 ^o C.

 The result is graphite with an ash content of 0.48%. To obtain graphite with an ash content of <0.1%, graphite is sent for re-purification, and all operations are carried out in the same sequence with the same parameters, except that 0.32 kg of a 50% NaOH solution is added per 1 kg of graphite during sintering; wash flow 2 m / h, the number of pulsations 30. The result is graphite with an ash content of 0.07%.

 The results obtained by the proposed method are summarized in table.

In all experiments, the specific consumption of the washing solution of 5.0-7.5% HNO ₃ was: for washing in a column of 5 l per kg of graphite per one stage of purification; a washing solution of H ₂ O 5 l per kg of graphite per 1 stage of purification.

 * A 40% alkali solution can also be used for sintering graphite, but in this case, the mass ratio of the solution to graphite should be recalculated proportionally.

Thus, the proposed method can significantly reduce material costs by reducing the energy intensity of the process (sintering is carried out at 350 ^o C instead of 950 ^o C, the process provides only one filtering operation), the intensification of the washing process, reducing the consumption of washing solutions and increasing the productivity of the process. The method also allows to achieve a high degree of purification: a single sintering of the initial graphite with an ash content of 7% leads to the production of graphite with an ash content of <0.5%, and with an increase in alkali consumption by 2 times with an ash content of up to 0.1%. When processing twice, the method allows to stably obtain graphite with an ash content of <0.1%.

Claims (5)

 1. The method of purification of natural graphite, including sintering graphite powder with an aqueous solution of an alkaline agent, subsequent washing with water and dilute acid and drying, characterized in that the washing of graphite is carried out by a countercurrent pulsating flow of the washing solution supplied at a speed of 1.7 - 3.0 m / h, and a pulsation frequency of 25 - 35 pulses per minute with a specific flow rate of 5 l / kg of graphite.  2. The method according to claim 1, characterized in that a 40-50% alkali solution is used as the alkaline agent. 3. The method according to claim 1, characterized in that the sintering is carried out at 350 ^o C.  4. The method according to claim 1, characterized in that 5.0 to 7.5% nitric acid is used as the diluted acid.  5. The method according to claim 1, characterized in that the washing of graphite is carried out first with dilute acid, and then with water.

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